This invention relates to a master-slave teleoperation control system in which a slave station responds to command signals from a master station by moving to positions defined by the master station, and the master station, in response to signals from the slave station, reflects forces encountered by the slave station.
A teleoperation control system is a system in which an operator at a master station can manipulate a control element such as an arm, hand, etc., and cause a similarly constructed slave element, such as an arm, hand, etc., located at a remote slave station to move in a certain way. Such systems are useful, for example, in hazardous environments such as in connection with nuclear reactors or other radioactive environments, in space, in deep water, etc. In all such systems, it is generally desirable that movement of the control or master element be exactly reflected in the slave element and that movement of the master element by the operator feel the same as if the operator were directly manipulating the slave element. Since the master element and slave element are typically located remotely from one another, control signals must be sent from the master station to the slave station, for example by radio, and similarly, reaction signals must be sent from the slave station to the master station if the "feel" by the master station of forces encountered at the slave station is to be achieved.
A number of arrangements have been proposed for teleoperation control systems in which feedback loops for position control of the slave element and force reaction of the master element are provided. One such system is disclosed in U.S. Pat. No. 4,661,032 and includes a type of asymmetric configuration substantially as shown FIG. 1. There, a master link element 104, of a master station, shown to be a joy stick, is coupled to an actuator 108, typically a motor or similar device. The position of the master link 104 is detected by a transducer 112 which produces a position signal for supply to a position control servomechanism 116 of a slave station. The force being applied to the master link 104 by the operator is detected by another transducer 120 and a force signal is produced for supply to a force control servomechanism 124 located at the master station.
The prior art asymmetric system FIG. 1 also includes a slave link 128, also a joy stick, coupled to an actuator 132, which typically would be a motor or motors for causing the slave link to move. Both actuators 108 and 132 are mounted on bases 110 and 134 respectively to hold them in place while either reacting to movement of a link or causing a link to move. As at the master station, the position of the slave link 128 and the force supplied to the slave link are detected by transducers 136 and 140 respectively. The transducer 136 supplies a position signal to the position control servomechanism 116 at the slave station and the transducer 140 supplies a force signal to the force control servomechanism 124 located at the master station.
The force control servomechanism 124 compares the force information received from transducers 120 and 140, produces an error signal indicating the difference between the two force information signals, amplifies the error signal and then signals the actuator 108 to cause it to either increase or decrease the force response to movement of the master link 104 to reflect either an increase or decrease respectively of force encountered by the slave link 128. Similarly, the position control servomechanism 116 compares position information signals received from transducers 112 and 136, produces and amplifies an error signal representing the difference between th position information signals, and supplies the amplified error signal to the actuator 132. The actuator 132, in response, causes movement of the slave link 128 to more closely approximate the position of master link 104.
In another prior art system, two force control servomechanisms are provided both at the slave station as well as at the master station, with each receiving one signal from a respective force transducer. The other signal received by both such force control servomechanisms is a position difference signal developed, for example, by a position control servomechanism similar to position control servomechanism 116 of FIG. 1. The outputs of the two force control servomechanisms, in such an arrangement, is then supplied directly to corresponding actuators at the master station and slave station. This type of system is sometimes referred to as a symmetric teleoperation control system.
Among the problems encountered with the asymmetric system is instability resulting when the slave link contacts some object or impedance, i.e., an oscillatory behavior causing reduction in the control capability. In the symmetric system, there tends to be drag or resistance in moving the master element even when the slave element is not in contact with or moving an object. That is, the unloaded operator input impedance is higher than desired. Also, the intersystem (between master and slave) stiffness is not as high as desired so that a springiness or yield is present in the master link even though the slave link may contact an immoveable object.
In general, it is desired that the "feel" at the master link in a teleoperation control system be the same as if there were a direct interaction between the master link and whatever objects or items are being manipulated by the slave link.